try{
    var docEl = document.documentElement,
    resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
    recalc = function () {
        var clientWidth = docEl.clientWidth;
        if (!clientWidth) return;
        docEl.style.fontSize = 100 * (clientWidth / 750) + 'px';
    };
    if (document.addEventListener){
        window.addEventListener(resizeEvt, recalc, false);
        document.addEventListener('DOMContentLoaded', recalc, false);
    }
} catch (e) {}